JPH01116433A - Measurement of concentration of fine particle by laser beam - Google Patents

Abstract

PURPOSE:To perform measurement or local measurement in a high speed flow field by a method wherein a laser beam is allowed to be incident on a particle to allow the evaporated substance from the particle to emit a beam while the emitted beam is spectrally diffracted to obtain a spectrum which is, in turn, used in the measurement of the particle. CONSTITUTION:The laser beam 1 emitted from a laser beam oscillator 9 is once diffused by a concave lens 11 and subsequently condensed by a condensing optical system 14 containing convex lenses 12, 13. A specimen 7 is placed at the position where said condensed laser beam 1 is received. The beam 4 emitted from the plasma generated in the vicinity of the surface of the particle of the specimen 7 is condensed by a condenser 15 to be incident on a spectroscope 5 and spectrally diffracted by the spectroscope 5 to obtain monochromatic beam which is, in turn, photoelectrically converted by a photomultiplier 16 to be amplified by an amplifier 17 and, thereafter, the change of the intensity of the beam with the elapse of time is recorded by an oscilloscope 18.

Description

[Detailed Description of the Invention] (a) Purpose of the Invention [Field of Industrial Application] This invention is applicable to the measurement of particle concentration and particle size, and the measurement of particle constituent substances in the exhaust of diesel engines, gas turbines, etc. or in clean rooms. This relates to a method for measuring particle size, such as identification.

[Prior Art] In recent years, environmental pollution has become a major social problem. For example, various types of exhaust from diesel engines, gas turbines, Stirling engines, etc.
It is necessary to control the constituent substances.

Conventionally used methods for measuring particle concentration, particle size, etc. in such cases are: (1) collecting particles with a filter etc. and observing them with a microscope etc. (2) dispersion system of particles (3) Inject light into a dispersion system of particles and detect the light scattered by the particles. (4) Measure particle size distribution using Fraunhofer diffraction. It is a method such as doing.

[Problems to be solved by the invention] However, (1) is a batch method, which can only perform measurements after combining temporally and spatially adjacent sections into one measurement, resulting in delayed response and In addition to not being able to perform local measurements, (2), which causes large disturbances to the field, can only measure the average value over the entire optical path length of the incident light, and (3) cannot distinguish between particle substances, and as the particle size becomes smaller, the S/N decreases. The ratio (signal to noise ratio) is low and inferior.

(4) is inappropriate for high-speed measurements Each has its own problems.

This invention was made in view of the above-mentioned circumstances, and it is possible to perform measurements in high-speed flow fields and local measurements without disturbing the field, has an extremely high S/N ratio, and can simultaneously measure particle concentration and particle size. The purpose of the present invention is to provide a method for measuring the concentration of particulates that enables the estimation of the amount of particles and, importantly, the ability to distinguish between particulate substances, which has not been possible in the past.

(B) Structure of the Invention [Means for Solving the Problem 1] Corresponding to this object, the method for measuring the concentration of particulates by laser emission of the present invention detects evaporated matter from the particles by injecting laser light into the particles. It is characterized by emitting light and measuring the particles based on the spectrum obtained by spectroscopy of the emitted light.

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

First, the principle of this measurement method will be explained with reference to FIG. Third
The figure shows the evaporation rate ff per pulse when pulsed laser light (YAG laser, wavelength 1.06 μm) is applied to the solid surface of carbon.
1 (μg/pulse), but at that time,
The output intensity of the pulsed laser beam was measured for each case in which the output intensity was varied from 0 to 1, with a maximum value of 1 at about 50011j, and the results were plotted and shown in a graph.

In Figure 3, when the output intensity of the pulsed laser beam exceeds a certain level (0.3 in the figure), the amount of carbon evaporated per pulse does not increase any more even if the output intensity increases; It has been shown that the value remains almost constant.

This means that if the output of the pulsed laser exceeds a certain intensity, 1
During a portion of the pulse, that is, from the start to a certain point, the solid surface becomes very hot and evaporation occurs, creating a plasma state near the solid surface, and subsequent light is blocked by this plasma and reaches the solid surface. It is thought that the amount of evaporation no longer increases as the amount of evaporation stops increasing, and instead the blocked laser light heats the plasma and a light emission phenomenon occurs with an intensity corresponding to the intensity of the laser light.

This emitted light shows different spectra depending on the constituent materials of the solid, and its intensity is proportional to the cross-sectional area of the particle. Therefore, monochromatic light obtained by spectroscopy of the emitted light when a laser beam of a certain intensity is incident on the particle. By measuring the intensity of the spectrum, it is possible to identify the constituent substances of the particles and find out the cross-sectional area of the particles into which the laser beam is incident.

Next, FIG. 2 shows a method of measuring particle a degree using laser emission according to the present invention.

First, the laser beam 1 of a certain intensity or more is incident on the particle 2 (FIG. 2(a)), and a plasma state is generated near the surface of the particle 2 by the evaporated material 3 from the particle 2. Light 4 is emitted (FIG. 2(b)). This light emission occurs within the time of one pulse when the laser beam 1 is a pulsed laser beam.

A photoelectric converter 20 receives a spectrum 6 obtained by condensing the light 4 and separating it with a spectroscope 5 .

When the particle 11 degree is dilute, such as the number of particles contained in the laser beam irradiation volume is 1 or less, the particle S degree can be measured by counting the number of times of light emission. Estimate the diameter.

On the other hand, when the particle concentration is high and a plurality of particles exist within the laser beam irradiation volume, the light is received by a photoelectric converter (for example, a matrix-like microchannel plate) having spatial resolution, and the particles that emit light simultaneously are counted. Further, as in the case where the particle S degree is dilute, the particle size is estimated from the emission intensity.

Furthermore, the light emitted from a plurality of types of particles having different constituent substances is spectrally dispersed, and the intensity of monochromatic light corresponding to each constituent substance is detected, and the concentration of each particle is distinguished and determined.

[Example] FIG. 1 shows a measuring device 10 for carrying out the method of measuring particulate concentration using laser emission according to the present invention. In the measuring device 10, a laser beam 1 emitted from a laser beam oscillator 9 is used.
Once the light is expanded by the concave lens 11, the convex lens 12
．． A condensing optical system 14 including 13 condenses the light. A sample 7 is placed at a position where it receives this focused laser beam 1 in a spot shape with a cross-sectional radius of 0.5 am to 0.8 Hn.

Luminescence 4 from the plasma generated near the surface of the particles of the sample 7 is collected by a condenser 15 and incident on the spectrometer 5.
The monochromatic light obtained by spectroscopy is photoelectrically converted by a photomultiplier 16, and after being amplified by an amplifier 17, the change in intensity over time is recorded by an oscilloscope 18. The oscilloscope 18 operates using the photodiode 21 as a trigger, so that a part of the light emission 4 is connected to the photodiode 21.
It is set to be number 1.

[Experiment example] Here, a carbon plate 7a is used as the sample 7, and is rotated at a constant speed by a motor 8 so that the incident position of the laser beam 1 on the carbon plate 7a moves at a constant speed, so that the surface of the carbon plate 7a is configured. The same carbon particles are successively incident on the laser beam 1 to simulate the flow motion of the particles. Using the measuring device 10, the laser beam 1 is incident on the carbon particles on the surface of the carbon plate 7a in the atmosphere, and the emitted light 4 at that time is spectrally separated)
The time-dependent changes in the intensity of the obtained spectra were recorded, and Figure 4 was obtained. That is, when a laser beam is incident on a carbon plate, a plasma state is generated near the surface of the carbon plate, and carbon C among the evaporated matter is
Monochromatic light with a wavelength of 248 nm appears corresponding to , a spectrum with a wavelength of 516 nm corresponds to C2, and a spectrum with a wavelength of 388 ru++ appears corresponding to CN, indicating that the light emission attenuates as this plasma state cools. ing.

[Function/Effect] In the experimental example, the laser beam 1 is incident on the carbon plate 7a rotating at a constant speed, but it is also possible to incident the laser beam on the dispersed particles, separate the emitted light, and record the intensity of the spectrum. In this case, the measurement device can be configured to compare the known data regarding the luminescence of the particles to identify the constituent substances of the particles, count the particles, measure the concentration of the particles, measure the particle size of the particles, etc. It is possible to perform measurements in high-speed flow fields and local measurements, the S/N ratio is extremely high, it is possible to estimate the particle size at the same time as the particle concentration, and most importantly, it is possible to measure particle materials, which was previously not possible. It is possible to obtain a method for measuring the concentration of fine particles that also makes it possible to differentiate them.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of a measuring device for performing the method of measuring particle concentration using laser emission according to the present invention on particles on a solid surface, and FIG. 2 shows the method of measuring particle concentration using laser emission according to the present invention. FIG. 3 is a graph showing the relationship between the carbon evaporation port per pulse (reduction in the thickness of the carbon plate per shot) and the intensity of the incident pulsed laser beam in the apparatus shown in FIG. and FIG. 4 is a graph showing changes over time in the intensity of monochromatic light recorded by making laser light incident on a carbon plate using the WA apparatus shown in FIG. 1... Laser light 2... Particle 3... Evaporated matter 4... Luminescence 5... Spectrometer 6... Spectrum 7... Sample 7a... Carbon plate 8... Motor 9 ...Laser light oscillator 10...Measuring device
11... Concave lens 12... Convex lens 13.
...Convex lens 14...Condensing optical system 15...
Concentrator 16...Photomultiplier 17...Amplifier 18...Oscilloscope 20...Photoelectric converter 21...Photodiode No. 11 Fig. 2 (a) (b)
(c) Figure 3
Vals racer 9th nest↑Target wind skin 4th time (μS)

Claims (1)

[Claims] A method for measuring the concentration of particulates by laser emission, characterized in that the evaporated matter from the particles is caused to emit light by injecting a laser beam into the particles, and the particles are measured by the spectrum obtained by dispersing the emitted light.